In an engine for a construction machine such as a bulldozer and a large dump truck, there may be a case that abrupt deceleration occurs from a driving state in a middle-high speed range and a middle-high load range. Specifically, in a case with a bulldozer, the above occurs when a decelerator pedal is depressed during a soil carrying operation at middle-high speed. In a case with a dump truck, the above occurs when an accelerator pedal is unintentionally returned while running uphill at middle-high speed in a sediment-loaded state.
In such a case, when an exhaust turbocharger is mounted on the internal combustion engine, as illustrated in FIG. 9, an operating point M1 of the exhaust turbocharger is shifted to an operating point M2 as passing on a locus indicated by a solid line from a middle-high speed range and middle-high load range side to a low speed range side so as to achieve matching with the engine at the operating point M2. The exhaust turbocharger rotates a turbine by using exhaust gas exhausted from the internal combustion engine and performs intake supercharging to the internal combustion engine by driving a compressor with rotational force of the turbine. Here, the horizontal axis of FIG. 9 denotes an intake flow rate of the exhaust turbocharger and the vertical axis of FIG. 9 denotes a pressure ratio of the compressor.
However, since the operating point temporarily enters into a surge area across a surge line at some midpoint while the operating point is shifted from the operating point M1 to the operating point M2 owing to abrupt deceleration, there occurs surging to destabilize operation of the exhaust turbocharger with fluctuation of intake pressure. This is because revolution of the exhaust turbocharger remains at high speed owing to inertia thereof despite a state that substantial amount of intake air is not required as the engine revolution speed being abruptly dropped as a result of depressing of a decelerator pedal or unintentional returning operation of an accelerator pedal. Then, the surging may cause strong self-exited vibration at the compressor side and may cause breakage in some cases.
Based on such a situation, there has been proposed an intake controller which lessens inflow resistance of intake air at an outlet passage side of the compressor as feeding intake air to an inlet passage side of the turbine from the outlet passage side of the compressor by controlling an open-close valve of an exhaust gas recirculation passage from a fully closed state into a fully opened state while using an exhaust gas recirculation passage reversely to normal use, in a case that the internal combustion engine is abruptly decelerated from a driving state in a middle-high speed range and a middle-high load range (see Patent Literature 1). According to such an intake controller, since entering of the operating point of the exhaust turbocharger into a surge area can be suppressed, surging occurrence at the exhaust turbocharger can be suppressed as the operating point of the exhaust turbocharger becoming to pass on a locus indicated by a two-dot chain line in FIG. 9, for example.